The present invention relates to a filter body, a sintered filter unit and to a method for the manufacture of a filter body and filtering unit. More particularly, the invention relates to a reliable, mobile and easily handled sintered filter unit to be used in systems for protecting enclosed spaces such as rooms, shelters, vehicles, tents, containers and the like, against the penetration of contaminated fluid.
As is known, air and other gases are usually filtered continuously, by causing the gas to pass through a thick filter medium by application of pressure or vacuum. In household applications, air filters are used in which the medium in the filter units may be glass fibers impregnated with oil for retaining removed dust particles. These filter units are replaced when they become clogged.
Filters may be classified according to the nature of the driving force causing the filtration, such as gravity filters, pressure filters and vacuum filters.
Many types of filters are known for filtering gases. One such filter, described in German Patent Application No. 3204022, uses a loose filling of granules of an adsorbent medium such as activated carbon, placed between a pair of porous walls that retain the granular material. The drawback of such a filter is the fact that there is no internal cohesion of any kind, neither of the granulate, its flow, nor its filtering properties in use; the problems of granulating the activated carbon, its flow and its filtering properties in use also being difficult to check.
In U.S. Pat. No. 3,645,072, there is described a filter formed by bonding and molding a granular activated carbon with a frame having U-shaped channels. The bonded, activated carbon body may be reinforced with a wire or other net, and may contain areas with reduced thickness in order to minimize pressure drop.
In U.S. Pat. No. 5,505,892, there is described a process for the manufacture of a filter unit made from a molded adsorbent element which is permeable to gases. Standard gas/liquid filters are made from a housing containing a loosely filled, mechanically compressed granulate. Granules of an adsorbent medium, preferably activated carbon, are mixed with a granular organic thermoplastic binder medium in a dry state. The resultant dry, granular mixture is put in a mold, compacted, and heated while substantially excluding air from it, to a temperature above the plastic range of the binder medium.
Standard gas/liquid filters are made of a rigid housing, containing loosely filled, mechanically compressed, fixed adsorbent granulate. The granulate is held under pressure between screens, using any spring system which requires a rigid, therefore quite expensive, housing. Such housings are usually made of metal. Furthermore, these filters must be installed only in a particular configuration, determined by the respective orientation. Normally, these filters are also sensitive to shock and other mishandling.
It is an object of the present invention to provide a simple, compact filter unit which can be safely and reliably used, even by untrained persons.
It is another object of the present invention to use known, standard materials which can be easily obtained.
In accordance with the present invention, there is therefore provided a solid filter body for a filter unit, comprising a sintered composition of adsorbing materials containing activated carbon having a particle size in the range of from 4 to 100 mesh, and a binder in the form of thermoplastic powder having a particle size in the range of from 10 to 250 mesh, the ratio of binder to adsorbent being less than 25% by weight; said composition being sintered at a temperature below 250xc2x0 C.
The invention further provides a fluid filter unit, comprising a casing having inlet and outlet openings housing a solid filter body made of a sintered composition of adsorbing materials containing activated carbon having a particle size in the range of from 4 to 100 mesh, and a binder in the form of thermoplastic powder having a particle size in the range of from 10 to 250 mesh, the ratio of binder to adsorbent being less than 25% by weight; said composition being sintered at a temperature below 250xc2x0 C.
The invention still further provides a method of manufacturing a solid filter body, said method comprising providing granulated adsorbing material containing activated carbon having a particle size in the range of from 4 to 100 mesh; providing a binder in the form of thermoplastic powder having a particle size in the range of from 10 to 250 mesh, the ratio of binder to adsorbent being less than 25% by weight; and sintering said adsorbing material and said binder at a temperature below 250xc2x0 C.